The general goal of this research project is to elucidate the molecular mechanisms involved in the repair of ionizing radiation damage using T4 bacteriophage and its Escherichia coli host as model systems. To this end, this laboratory is proceeding to purify the products of the T4x and y genes as well as the Escherichia coli x-ray endonuclease. In addition, in vitro repair studies will be carried out on damaged DNA substrates using purified enzymes of known specificity. BIBLIOGRAPHIC REFERENCES: Katcher, H. and Wallace, S. (1976). Partial purification of the X-ray endonuclease of Escherichia coli. Radiat. Res. 67:573. Armel, P., Strniste, G., and Wallace, S. (1977). Studies on X-ray endonuclease specificity: Roles of hydroxyl and reducing radicals in the production of DNA lesions. Radiat. Res. Feb.